In order to start a combustion engine, notably that of a motor vehicle, it is known practice to use a starter provided with a starter drive assembly capable of transmitting a rotational energy from the starter to a starter ring gear of a combustion engine. This starter drive assembly is mounted with the ability to slide on a driveshaft, which is coupled to the shaft of an electric motor via speed-reducing gearing.
The starter drive assembly is able to move between an active position in which a drive pinion meshes with the starter ring gear in order to start it following activation of the ignition, and a rest position in which the drive pinion is situated some distance away from the engine ring gear.
For that purpose, as may be seen in FIG. 1, the starter drive assembly 1 comprises the drive pinion 2 mounted to rotate as one with a pinion body 3, which is slidingly mounted on the drive shaft 5. The pinion body 3 is driven, via a freewheel device 8, via a driver 6 intended to be activated by a control lever 7.
The problem with such a configuration is that the variable-volume chamber 9 extending between one end of the drive shaft 5 and an end of the pinion body 3 opposite generates a retaining force as the starter drive assembly I moves, and this may cause problems with the meshing of the pinion 2 in the starter ring gear.
What happens, as the starter drive assembly 1 moves from the rest position into the active position, is that the increase in the volume of air contained in the chamber 9 as a result of the pinion body 3 moving further away with respect to the drive shaft 5 generates a suction effect. Moreover, as the starter drive assembly 1 moves from the active position into the rest position, the reduction in the volume of air contained in chamber 9 as a result of the pinion body 3 moving closer to the drive shaft 5, generates a resistive compression force. It should be noted that the generation of retaining forces is amplified by the fitting of bearing bushings 10 between the drive shaft 5 and the pinion body 3, as these are oiled and therefore cause the volume of air of the chamber 9 to be even better trapped with respect to the external atmosphere.
The system described in document EP1298317 allows the creation of a communication between the variable-volume chamber and a space situated near the freewheel device, by the creation of superficial grooves on an internal periphery of the pinion body. However, such a system requires the development of a complex tool in order to be able to create the pinion body by cold heading. Furthermore, the pinion body is mechanically weakened as a result of the creation of the grooves along its entire length.